I would sincerely not recommend Dual Xeon builds as they much more expensive than it is useful.
I own a dual
Intel® Xeon® Processor E5-2680 v2 (25M Cache, 2.80 GHz) / Asus Z9PE-D8 WS / 128 Gb DDR3 ECC RAM / Nvidia GTX Titan 6Gb GDDR5 / El Capitan 10.11.3 build and i'm very disappointed with the poor performances / cost ratio of this build.
• Most programs are not optimized for this kind of build in their Mac OS version at least : After Effects / Première / Nuke and many other video editing or vfx programs use only 10 to 40 % of the processing available. Same thing with encoding software such as Episode / FFMpeg / Compressor etc.
• For Audio Workstations (DAO) the latency is way better on single CPU builds and ProTools and such are not optimized for this as well. I recommend single i7 2011v3 5960X and as much DDR4 non-ECC RAM as possible (128 Gb is possible with Asus X99-E WS).
• As GeekBench runs well and scores high (49500 with 20 cores / 40 threads) and uses all CPU cores I suspect it's just a matter of software optimisation and it's not system related. I think this build would make a terrific WebServer but who cares about Apple Server these days...
You have been warned : better buy two hackintoshes and have great support from the community than one big fat one that will drain your time and money for almost nothing.
PM!